U.S. patent number 11,329,536 [Application Number 16/558,652] was granted by the patent office on 2022-05-10 for electrical machine winding assembly and method of manufacture thereof.
This patent grant is currently assigned to Rolls-Royce plc. The grantee listed for this patent is ROLLS-ROYCE plc. Invention is credited to Jameel B. Khan, Alexis Lambourne, Alexander C. Smith.
United States Patent |
11,329,536 |
Khan , et al. |
May 10, 2022 |
Electrical machine winding assembly and method of manufacture
thereof
Abstract
A method of manufacturing a winding assembly for an electrical
machine, the method comprising: selecting (S1) a mathematical
function defining the spatial separation between adjacent turns of
a winding path, the mathematical function dependent on one or more
parameters of the electrical machine and/or of the anticipated
operating environment of the electrical machine; forming (S2), by
three-dimensional, 3D, printing, an electrically insulating body
comprising a channel defining the winding path in accordance with
said function, the channel having an inlet and an outlet; heating
(S3) the electrically insulating body to a temperature above the
melting point of an electrically conducting material; flowing (S4)
the electrically conducting material through the inlet to the
outlet to fill the channel; and cooling the electrically insulating
body to solidify the electrically conducting material within the
channel, thereby forming said winding assembly.
Inventors: |
Khan; Jameel B. (Manchester,
GB), Lambourne; Alexis (Belper, GB), Smith;
Alexander C. (Holmfirth, GB) |
Applicant: |
Name |
City |
State |
Country |
Type |
ROLLS-ROYCE plc |
London |
N/A |
GB |
|
|
Assignee: |
Rolls-Royce plc (N/A)
|
Family
ID: |
64024322 |
Appl.
No.: |
16/558,652 |
Filed: |
September 3, 2019 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
|
US 20200119628 A1 |
Apr 16, 2020 |
|
Foreign Application Priority Data
|
|
|
|
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Sep 20, 2018 [GB] |
|
|
1815304 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02K
3/50 (20130101); H02K 15/12 (20130101); H02K
3/02 (20130101); H02K 3/30 (20130101); H02K
3/18 (20130101); H02K 1/18 (20130101); H01F
5/02 (20130101); H02K 3/34 (20130101); H02K
15/0407 (20130101); H02K 3/04 (20130101); H02K
15/00 (20130101); H01F 41/125 (20130101); H02K
3/32 (20130101); H01B 3/12 (20130101); B33Y
80/00 (20141201) |
Current International
Class: |
H02K
15/04 (20060101); H02K 3/50 (20060101); H02K
1/18 (20060101); H02K 3/02 (20060101); H02K
3/30 (20060101); H02K 3/34 (20060101); B33Y
80/00 (20150101); H02K 15/12 (20060101); H01B
3/12 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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104242522 |
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Dec 2014 |
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CN |
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102014106851 |
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Nov 2015 |
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DE |
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3142229 |
|
Mar 2017 |
|
DE |
|
3113333 |
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Jan 2017 |
|
EP |
|
3142229 |
|
Mar 2017 |
|
EP |
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2018117477 |
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Jul 2018 |
|
JP |
|
20160119424 |
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Oct 2016 |
|
KR |
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2018147244 |
|
Aug 2018 |
|
WO |
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Other References
Extended EP Search Report dated Dec. 19, 2019 and issued in
connection with European Patent Application No. 19192444.8, 8
pages. cited by applicant .
Extended European Search Report, European Application No.
21155933.1-1201 dated Feb. 26, 2021, 10 pages. pages. cited by
applicant .
Great Britain search report dated Feb. 25, 2019, issued in GB
Patent Application No. 1815302.3. cited by applicant .
Great Britain search report dated Jun. 11, 2019, issued in GB
Patent Application No. 1815304.9. cited by applicant .
Great Britain search report dated Feb. 25, 2019, issued in GB
Patent Application No. 1815304.9. cited by applicant .
M. Sajid et al. "Impulse and Fast Surge Distribution of Voltage in
11 kV Industrial Motor" 2016 International Conference an
Electrical, Electronics, and Optimization Techniques (ICEEOT),
Chennai, 2016, pp. 215-219. cited by applicant.
|
Primary Examiner: Patel; Tulsidas C
Assistant Examiner: Stout; Riley Owen
Attorney, Agent or Firm: Barnes & Thornburg LLP
Claims
The invention claimed is:
1. A method comprising manufacturing a winding assembly for an
electrical machine, the method comprising: selecting a function
defining a spatial separation between adjacent turns of a winding
path, the function dependent on one or more parameters of the
electrical machine and/or an anticipated operating environment of
the electrical machine; forming, by three-dimensional, 3D,
printing, an electrically insulating body comprising a channel
defining the winding path following the function, the channel
having an inlet and an outlet; heating the electrically insulating
body to a temperature above the melting point of an electrically
conducting material; flowing the electrically conducting material
through the inlet to the outlet to fill the channel; and cooling
the electrically insulating body to solidify the electrically
conducting material within the channel, thereby forming said
winding assembly, wherein the one or more parameters include one or
more of: a winding inductance; a winding capacitance; a winding
resistance; a dielectric strength of the material forming the
electrically insulating body; an anticipated operating temperature
and/or pressure of the electrical machine; a peak supply voltage to
the electrical machine; a rise time of the supply voltage to the
electrical machine; and a frequency of the supply voltage to the
electrical machine.
2. A method comprising manufacturing a winding assembly for an
electrical machine, the method comprising: selecting a function
defining a spatial separation between adjacent turns of a winding
path, the function dependent on one or more parameters of the
electrical machine and/or an anticipated operating environment of
the electrical machine; forming, by three-dimensional, 3D,
printing, an electrically insulating body comprising a channel
defining the winding path following the function, the channel
having an inlet and an outlet; heating the electrically insulating
body to a temperature above the melting point of an electrically
conducting material; flowing the electrically conducting material
through the inlet to the outlet to fill the channel; and cooling
the electrically insulating body to solidify the electrically
conducting material within the channel, thereby forming said
winding assembly, wherein the function defines a graded spatial
separation between adjacent turns of the winding path.
3. The method of claim 2, wherein the spatial separation reduces
from a maximum at an end of the winding path to a nominally
constant separation at a predetermined distance along the winding
path.
4. The method according to claim 1, wherein the function defines a
larger average spatial separation between first and second turns of
the winding path than between the second and subsequent turns of
the winding path.
5. The method according to claim 1, wherein the function is based
on a model of partial discharge within the electrical machine and
the spatial separation between adjacent turns of the winding path
defined by the function is calculated to minimize the probability
of partial discharge occurring.
6. The method according to claim 1, wherein the channel is formed
internally to the electrically insulating body and the inlet and
outlet are formed at the surface of the electrically insulating
body, such that the channel extends continuously through the
electrically insulating body.
7. The method according to claim 1, wherein the electrically
insulating body is formed by 3D printing with a ceramic
material.
8. The method according to claim 1, wherein the electrically
conducting material is copper and the electrically insulating body
is heated to a temperature greater than 1100 degrees Celsius,
preferably around 1300 degrees Celsius, prior to and during the
step of flowing the electrically conducting material.
9. The method according to claim 1, further comprising prior to the
step of flowing the electrically conducting material, vibrating the
electrically insulating body and/or applying a gas stream to the
inlet to remove any debris from the channel via the outlet.
10. The method according to claim 1, further comprising applying a
lower pressure to the outlet relative to a pressure at the inlet
during the step of flowing the electrically conducting
material.
11. The method according to claim 1, wherein the channel is
substantially evacuated during the step of flowing the electrically
conducting material.
12. The method according to claim 1, wherein the function defines a
graded spatial separation between adjacent turns of the winding
path.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority
from British Patent Application No. GB 1815304.9, filed on 20 Sep.
2018, the entire contents of which are herein incorporated by
reference.
BACKGROUND
Technical Field
This disclosure relates to electrical machines and in particular to
a winding assembly for an electrical machine and a method of
manufacturing same.
Description of the Related Art
Conventional electrical machine design has certain temperature
limitations. These limitations are typically set by the insulation
system used on the windings/coils in the electrical machine, which
may be a generator or a motor, for example. Electrical machine
windings may be on the rotor, on the stator or on both, and
typically comprise several turns of an electrically conducting
wire, such as copper, wound around a soft magnetic tooth (pole).
The electrically conducting wire is coated with an electrically
insulating medium to prevent short circuits from occurring: within
the winding (turn to turn insulation), between phases (phase to
phase insulation) and between the winding and the tooth (phase to
earth insulation).
In many electrical machines the insulation is provided by a polymer
coating on the copper wire. Polymer-coated wire is rated according
to the time that it is able to operate at a particular temperature,
e.g. class H wire can operate for 20 000 hours at 180 degrees
Celsius, whereas class M wire can operate for 20 000 hours at a
higher temperature of 220 degrees Celsius. Class C, rated at up to
240 degrees Celsius, represents the best thermal capability in
commonly available electric wires for electrical machines. At
temperatures above 220 degrees Celsius there is an approximation
that for every 10 degrees Celsius increase in temperature, the
lifetime of the insulation is halved, i.e. at 230 degrees Celsius a
class M wire will only last 10 000 hours. Thus for most high
temperature motor/generator applications the temperature limit is
220 degrees Celsius and if the operating environment or
self-heating of the machine creates a temperature greater than this
the motor/generator should be actively or passively cooled to keep
the wire temperature at or below 220 degrees Celsius.
For applications requiring an operating temperature above 220
degrees Celsius, ceramic insulated wires are available. Ceramic
insulators have a better temperature capability than polymers.
However they are not as flexible, they suffer from thermal
expansion mismatch with the copper wire and they can crack with
rapid heating (thermal shock). For one or more of these reasons,
whilst ceramic insulated wires are in principle available, they are
rarely chosen for use in electrical machine applications as the
lifetime can be short due to failure modes such as crackling,
thermal shock, etc.
In addition, the evolution of the power semiconductor has led to
high switching frequencies of transistors employed in modern
converter topologies used in conjunction with electric motors.
Depending on the control characteristics (gate resistors,
capacitors, voltage commands) and the pulse width modulation (PWM)
scheme adopted, combined with the impedance of the cable leading to
the electric motor and the winding itself, repetitive overvoltage
on the motor terminals may result. The use of PWM may degrade the
electrical insulation between turns of the motor windings and
possibly reduce the motor lifetime. The impedance of the cables
leading to the electric motor and the winding itself can be
considered as a RLC (resistance, inductance and capacitance)
circuit. When the values of the effective RLC circuit are such that
the peak voltage exceeds the supply voltage, the circuit response
to this excitation is defined as an overshoot. The overshoots
affects the electrical insulation between adjacent turns of the
winding and is dependent on several factors, such as the rise time
of the voltage pulse applied to the motor according to the PWM
scheme chosen, the length of cable leading from the voltage supply
to the electrical machine, the minimum time separation between
adjacent voltage pulses according to the PWM scheme chosen and the
switching frequency.
The overshoot typically affects only, or substantially only, the
first turn of the winding with respect to the point at which the
voltage is applied to the electric motor winding. This is because
the inductive and capacitive properties of the winding dampen the
voltage pulse as it propagates through the winding from the input
to the output--thereby decreasing its peak value. The faster the
rise time of the applied voltage pulse (i.e. the greater the value
of dV/dt) the more significant the overshoot effect is and
therefore the greater the voltage difference which is observed
between adjacent turns of the winding, e.g. between the first turn
and the second turn of the winding. Thus faster rise times lead to
a greater chance of electrical breakdown, known as partial
discharge, occurring within the winding of the electrical
machine.
Partial discharge is a small electrical spark (arc) that occurs
within the insulation between turns of a winding. Each discrete
partial discharge event is the result of an electrical breakdown of
an air pocket within the insulation. Partial discharge will slowly
erode a polymer insulation material. Over time, partial discharge
can degrade the insulation to the extent that it will result in a
full short circuit failure of the electrical machine. Partial
discharge is particularly likely to be a problem in high frequency
converter fed electrical machines where the voltage rise time for
each energisation of a pole is very short (i.e. a large value of
dV/dt). Around 40 percent of the input voltage is observed between
the first two turns of the winding of an electric motor when the
voltage pulse rise time is on the order of 200 nanosecond to 1
microsecond, a value typical of PWM inverters.
SUMMARY
According to a first aspect there is provided a method of
manufacturing a winding assembly for an electrical machine, the
method comprising:
selecting a function defining a spatial separation between adjacent
turns of a winding path, the function dependent on one or more
parameters of the electrical machine and/or of an anticipated
operating environment of the electrical machine;
forming, by three-dimensional, 3D, printing, an electrically
insulating body comprising a channel defining the winding path in
accordance with the function, the channel having an inlet and an
outlet;
heating the electrically insulating body to a temperature above the
melting point of an electrically conducting material;
flowing the electrically conducting material through the inlet to
the outlet to fill the channel; and
cooling the electrically insulating body to solidify the
electrically conducting material within the channel, thereby
forming said winding assembly.
In the first aspect the winding assembly is manufactured by first
3D printing (also known in the art as additive manufacturing) the
insulation such that a winding path is defined by a channel, and
then subsequently introducing an electrically conducting material
into the channel to form the winding. Advantageously, 3D printing
can be carried out with a wide range of materials and the shape and
location of the channel defining the winding path can be precisely
controlled in the 3D printing process. Many electrically conducting
materials are difficult to 3D print but this issue may be overcome
by 3D printing the insulation first and then subsequently adding
the electrically conducting material, as per the first aspect. By
employing a 3D printing process to make the electrically insulating
body, the shape or cross section of the channel can be made
precisely as desired in order to accommodate an insulation gradient
where partial discharge risk is mitigated by increased insulation
thickness on initial turns of a coil. Further, the electrically
insulating body can be shaped around the channels in order to
improve heat transfer to the environment, e.g. by forming the body
with fins or other projections to increase surface area for heat
exchange. This helps to manage heat transfer from the coil to the
environment and also manages power loss within the windings.
The step of forming the electrically insulating body may comprise
firing the 3D printed body to densify the electrically insulating
body prior to introduction of the electrically conductive material.
The electrically insulating body may for example be formed from a
refractory ceramic material such as alumina, which generally
requires firing temperatures in excess of 1400 degrees Celsius,
i.e. well above the melting temperature of electrically conductive
materials such as copper.
The spatial separation between adjacent turns of the winding path
is defined by a selected function which enables parameters such as
dV/dt to be taken into account. 3D printing is well suited to
creating structures in accordance with such functions. Selecting
the spatial separation in accordance with a function also allows
the packing factor of the winding assembly to remain within a
reasonable tolerance, i.e. because not all turns of the winding
require a greater separation, e.g. a graded separation may be
defined by a function instead.
The one or more parameters may include one or more of:
a winding inductance;
a winding capacitance;
a winding resistance;
a dielectric strength of the material forming the electrically
insulating body;
an anticipated operating temperature and/or pressure of the
electrical machine;
a peak supply voltage to the electrical machine;
a rise time of the supply voltage to the electrical machine;
and
a frequency of the supply voltage to the electrical machine.
The function may define a graded spatial separation between
adjacent turns, such as the first two turns, of the winding path.
The spatial separation may for example reduce from a maximum at an
end of the winding path to a nominally constant separation at a
predetermined distance along the winding path. As discussed above,
the probability of partial discharge is likely to be greatest
between the first two turns of the winding and may advantageously
be substantially or completely eliminated by choosing a graded
spatial separation between the first two turns of the winding path.
The function may define a constant spatial separation between at
least the last two turns of the winding path.
The function may define a larger average spatial separation between
the first two turns of the winding path than between the second and
subsequent two turns of the winding path. Partial discharge is more
likely to occur between the earlier turns of the winding than
between the latter turns of the winding, with respect to where the
voltage is applied. In this manner the probability of partial
discharge is reduced for the earlier turns of the winding whilst
retaining a more compact separation of turns of the winding for the
latter turns of the winding.
The function may be based on a model of partial discharge within
the electrical machine. The spatial separation between adjacent
turns of the winding path defined by the function may be calculated
to minimize the probability of partial discharge occurring.
The channel may be formed internally to the electrically insulating
body. The inlet and outlet may be formed at the surface of the
electrically insulating body, such that the channel extends
continuously through the electrically insulating body.
The electrically insulating body may be formed by 3D printing with
a ceramic material. As set out above, ceramic material, when used
as a winding electrical insulation, allows for higher temperature
operation of the electrical machine since its melting point can be
far greater than a conventional polymer coating. Furthermore, by 3D
printing the ceramic material, many of the prior known issues with
such coatings, e.g. lack of flexibility, can be overcome or
ameliorated. The winding assembly formed by 3D printing with a
ceramic material is particularly suitable for use at high
temperatures and for high voltage electrical machines.
The electrically conducting material may be copper, silver or
aluminium or an alloy thereof of any of these. The electrically
insulating body may be heated to a temperature greater than 1100
degrees Celsius, preferably around 1300 degrees Celsius, prior to
and during the step of flowing the electrically conducting
material. Copper is an excellent electrical conductor and by
heating the electrically insulating body to a temperature above the
melting point of copper it is able to flow freely into the channel
of the electrically insulating body defining the winding path
thereby filling the channel without leaving voids.
The method may further comprise, prior to the step of flowing the
electrically conducting material, vibrating the electrically
insulating body and/or applying a high-pressure gas stream to the
inlet to remove any debris from the channel via the outlet. This
helps to ensure the winding path defined by the channel is clear to
enable a smooth flowing of the electrically conducting material
into the channel.
The method may further comprise applying a lower pressure to the
outlet relative to the pressure at the inlet during the step of
flowing the electrically conducting material. This aids the
electrically conducting material to flow through the channel from
the inlet to the outlet and may speed up the process. Further, if a
pressurized inert gas is used then the copper is less likely to
oxidise.
The channel may be substantially evacuated during the step of
flowing the electrically conducting material. This helps to ensure
the material fully fills the channel and does not oxidise or pick
up other contaminants from the atmosphere within or around the
winding assembly.
According to a second aspect there is provided a winding assembly
for an electrical machine, the winding assembly comprising a
monolithic electrically insulating body having a first channel
defining a first winding path, the first channel being filled with
an electrically conducting material, wherein the average spatial
separation between the first two turns of the first winding path is
larger than the average spatial separation between the last two
turns of the first winding path
Since the electrically insulating body is monolithic (i.e. a
single, materially-continuous piece) it is strong and less prone to
failure through thermal shock and the like. In addition, the
average spatial separation between the first two turns of the
winding path being larger means that the probability for partial
discharge to occur between the first two turns is reduced.
The spatial separation between the first two turns of the first
winding path may be graded. The spatial separation between the last
two turns of the first winding path may be constant.
The first channel may be internal to the electrically insulating
body, such that the first channel is contiguous on all sides with
the electrically insulating body. An inlet and an outlet may be
provided at the surface of the electrically insulating body.
The electrically insulating body may be formed of a ceramic
material. The electrically conducting material may be copper.
Ceramic is an excellent electrically insulator and copper is an
excellent electrical conductor. Since ceramic has a higher melting
point than conventional polymer insulation, an electrical machine
employing a winding assembly according to the first aspect and with
ceramic insulating material can operate in a high temperature
environment without requiring cooling.
The winding assembly may further comprise a second channel defining
a second winding path, the second channel being filled with an
electrically conducting material, wherein the first and second
channels are mutually DC electrically insulated by the electrically
insulating body.
The first and second channels may together define a bifilar
winding.
The winding assembly may further comprise a cavity for receiving a
stator tooth.
According to a third aspect there is provided an electrical machine
comprising a stator, a rotor and one or more winding assemblies
according to the second aspect.
According to a fourth aspect there is provided an electric
propulsor comprising a fan and an electric motor connected to a
drive shaft and arranged to drive the fan, wherein the electric
motor comprises a winding assembly according to the second
aspect.
The electric propulsor may further comprise a gearbox connected to
receive an input from the electric motor and to output drive to the
fan so as to drive the fan at a lower rotational speed than the
electric motor.
According to a fifth aspect there is provided an aircraft
propulsion system comprising an electric propulsor according to the
fourth aspect.
DESCRIPTION OF THE DRAWINGS
Embodiments will now be described by way of example only with
reference to the accompanying drawings, which are purely schematic
and not to scale, and in which:
FIG. 1 is a sectional side view of an example hybrid electric
aircraft propulsion system;
FIG. 2 illustrates a winding assembly mounted on a tooth;
FIG. 3 illustrates channels of an electrically insulating body of a
winding assembly prior to filling with an electrically conducting
material;
FIG. 4 illustrates channels of an electrically insulating body of a
winding assembly after filling with an electrically conducting
material;
FIG. 5 illustrates a graded spatial separation between turns of a
winding assembly; and
FIG. 6 is a flowchart corresponding to a method of manufacturing a
winding assembly.
DETAILED DESCRIPTION
A schematic diagram of a basic hybrid electric aircraft propulsion
system 100 is shown in FIG. 1. An electric propulsion unit, or
engine, 101 comprises a fan 102 connected to an electric motor 103
by a central shaft 104. As with a conventional gas turbine engine,
the engine 101 comprises a nacelle 105 surrounding the fan 102 and
motor 103. The engine 103 is provided with electric power via power
electronics in a controller 106, which is connected to an electric
storage unit 107, which may include a battery, a supercapacitor or
a combination of the two.
The controller 106 is also connected to a generator 108 and a gas
turbine engine 109. The gas turbine engine 109 drives the generator
108 to generate electric power, which the controller 106
distributes between the electric storage unit 107 and the electric
motor 103. Under some conditions, the electric motor 103 may also
act as a generator, for example when a reduction in thrust is
demanded and the forward movement of the engine 101 drives the fan
102 until a required fan speed is reached. Energy may then be taken
from the motor 103 and stored in the electric storage unit 107.
The controller 106 takes inputs from the aircraft control system
(not shown), which provides a thrust or fan speed demand. The
controller 106 then manages how the demand is achieved, by
balancing use of the gas turbine engine 109 and generator 108 with
the electric storage unit 107. For example, when a step increase in
demand is received, the controller 106 may use the electric storage
unit 107 to provide an immediate increase in electric power to the
motor 103, while the gas turbine engine 109 is powered up more
slowly to accommodate for the different behaviour of the gas
turbine 109. Once the gas turbine engine 109 has reached a required
power output level, the balance of power taken from the generator
108 and electric storage unit 107 can shifted so that all of the
electric power comes from the generator 108, and an additional
amount can be used to recharge the electric storage unit 107.
The generator 108 and electric motor 103 of the hybrid electric
aircraft propulsion system 100 are two examples of electrical
machines. Electrical machines such as electric motor 103 and
generator 108 generally contain of a plurality of coils/windings
each formed of a number of electrically insulated turns of an
electrically-conducting wire forming a winding assembly. The
winding assembly may be provided on the stator, rotor or both.
FIG. 2 illustrates an electrical machine winding assembly 200
according to the present disclosure. The winding assembly 200 is
shown in situ on a magnetic tooth 210 of a rotor or stator 212
forming part of an electrical machine such as an electric motor or
generator described above with reference to FIG. 1. The winding
assembly consists of an electrically insulating body 202 formed of
e.g. ceramic or another electrically insulating material. The
winding assembly 200 also has a central cavity 216 which is shaped
to receive the tooth of a stator 212 or rotor on which the winding
assembly is to be located.
The electrically insulating body 202 is formed by 3D printing the
ceramic material. In this manner, the electrically insulating body
202 can be formed with a channel 204 defining a winding path, shown
in FIGS. 3 and 4. The channel 204 is preferably internal to the
insulating body 202 such that it is contiguous on all available
sides with the electrically insulating body 202. The channel 204
has an inlet (or runner) 206 and an outlet (or riser) 208 at the
surface of the electrically insulating body 202. Since the
electrically insulating body 202 is 3D printed, it is effectively a
single, materially continuous, i.e. monolithic, piece. This makes
it strong and less prone to failure through thermal shock and the
like.
In FIG. 3 the channel 204 is hollow whereas in FIG. 4 the channel
204 is shown filled with an electrically conducting material 214,
such as copper. The channel 204 is filled with the electrically
conducting material 214 by first heating the electrically
insulating body 202 to a temperature above the melting point of the
electrically conducting material 214. For example, if copper is
used as the electrically conducting material 214 then the
electrically insulating body 202 is heated to a temperature in
excess of 1000 degrees Celsius, preferably 1300 degrees Celsius.
Then, once the electrically insulating body 202 and the channel 204
within it have reached a temperature above the melting point of the
electrically conducting material 214, molten electrically
conducting material 214 is flowed into the channel 204 via the
inlet 206 to fill the channel 204 through to the outlet 208. Once
the channel is full with electrically conducting material 214 the
winding assembly 200 is cooled down in order to solidify the
electrically conducting material 214 within the channel 204 to
thereby form the winding. The inlet 206 and outlet 208 then serve
as electrical terminals for the winding in order to connect it to
adjacent windings or to a power supply, for example.
In the winding assembly 200 of FIGS. 3 and 4, the separation
between the first two turns of the channel 204 defining the winding
is x.sub.0+x whereas the separation between the final two turns of
the channel 204 defining the winding is x.sub.0, i.e. less than the
separation between the first two turns of the channel 204 defining
the winding path. In a practical implementation, the number of
turns of the winding will be greater than that shown. In a general
aspect, the spacing between the first and second turns of the
winding is greater than between the second and subsequent turns of
the winding. The spacing may be graded along the length of the
winding.
In the case that the electrical machine is an electrical motor, the
input voltage is applied at the first turn. In this manner, the
first turns of the winding may experience an overshoot as described
above and thus the electrically insulating body 202 of the winding
assembly 200 is more prone to the phenomenon of partial discharge
within the region between the first two turns of the winding
defined by the channel 204. In other words, when input voltage is
applied at the input 206 rather than at the output 208, the
potential difference between the first two turns of the winding
will be larger than the potential difference between the last two
turns of the winding when an input voltage pulse is applied, due to
the overshoot phenomenon described above, i.e. because the pulse
becomes temporally more spread out as it propagates through the
winding from the first turn to the last turn.
The spatial separation between adjacent turns of the winding path
defined by the channel may follow a function which is dependent on
one or more parameters of the electrical machine and/or of the
anticipated operating environment of the electrical machine, such
as, but not necessarily limited to: the winding inductance; the
winding capacitance; the winding resistance; the dielectric
strength of the material forming the electrically insulating body
202; the anticipated operating temperature and/or pressure of the
electrical machine employing the winding assembly 200; the peak
supply voltage to the electrical machine employing the winding
assembly 200; the rise time of the supply voltage to the electrical
machine employing the winding assembly 200 (i.e. dV/dt); and/or the
frequency of the supply voltage to the electrical machine.
The function may specify a constant additional separation between
the first turns of the winding, or may be more complex in nature,
e.g. specifying a graded separation which tapers from a larger
separation at the input to a constant separation after a set number
of turns, for example after one turn, of the winding. The constant
separation may be the same as the separation between the final two
turns of the winding. In general, the function defines a winding
path such that the average spatial separation between the first two
turns of the winding is greater than the average spatial separation
between subsequent turns of the winding--to mitigate the effect of
overshoot described above. For example, if the first two turns have
a graded separation going from x.sub.0+x to x over the length of
one complete turn of the winding and the final two turns have a
constant separation of x then the average separation between the
first two turns will be 0.5x.sub.0+x and the average separation
between the final two turns will be x.
Referring to FIG. 5, an example schematic plot of a voltage
amplitude signal as a function of distance along a coil is shown in
a top portion of FIG. 5, and a corresponding schematic illustration
of a conductor 501 surrounded by an insulating layer 502 of
variable thickness is shown in a bottom portion of FIG. 5. A
maximum increase in insulation thickness, m, is determined based on
the maximum overshoot voltage, .DELTA.V, The distance, d.sub.1,
over which the insulation thickness reduces to a nominal thickness,
n, is determined by the inductance, capacitance and insulation
thickness of the coil, as well as the overshoot voltage and the
temperature envelope. An angle of graduation, .theta., may be
defined as the decay of the overshoot voltage to a steady state.
Various mathematical equations can be derived to calculate the
voltage stress each turn of the coil will see, based on the
specific coil parameters and the voltage waveform data. Examples of
such equations and calculations are disclosed by M. Sajid et al, in
"Impulse and fast surge distribution of voltage in 11 kV industrial
motor," 2016 International Conference on Electrical, Electronics,
and Optimization Techniques (ICEEOT), Chennai, 2016, pp. 215-219
doi: 10.1109/ICEEOT.2016.7755049.
In the simple example shown in FIG. 5, the reduction in insulation
thickness is approximated by a linear function, such that the
insulation thickness, t, at a distance d along the conductor
length, is defined as:
.times..ltoreq.>.times..times. ##EQU00001##
The above function therefore provides in general terms a graded
spatial separation between adjacent turns of the winding path of a
coil, such that the spatial separation reduces from a maximum at an
end of the winding path to a nominally constant separation at a
predetermined distance along the winding path. In the example
shown, the graded spatial separation is a linear reduction in
separation between adjacent turns. In other examples the graded
spatial separation may be non-linear. Other functions may for
example be defined, such as an exponentially decaying function, to
more closely approximate the reduction in voltage stress along the
conductor length. In general terms, the average spatial separation
between the first and second turns of the winding path will be
greater than between the second and subsequent turns.
Before the molten electrically conducting material 214 is flowed
into the channel 204 it may be advantageous to vibrate the
electrically insulating body 202 and/or apply a high-pressure gas
flow from the inlet 206 to the output 208 in order to remove any
debris from the channel 204. Such debris may be, for example, loose
ceramic dust or fragments within the channel 204 left over from the
3D printing process used to form the electrically insulating body
202 or any other foreign bodies which may otherwise prevent a
smooth flowing of the electrically conducting material 214 into the
channel 204.
In order to assist the flowing of the molten electrically
conducting material 214 into the channel 204, the pressure at the
outlet 208 may be held lower than the pressure at the inlet 206 in
order to effectively draw the molten electrically insulting
material 214 through the channel 204 from the inlet 206 to the
outlet 208. Alternatively the flowing in of the electrically
conducting material 214 may be done in vacuum or near vacuum
conditions in order to prevent oxidation or contamination of the
electrically conducting material from contaminants in the
atmosphere.
The winding assembly 200 with the channel 204 filled with copper
may operate at temperatures up to approximately 1000 degrees
Celsius without being subject to deleterious phenomena such as
partial discharge. Winding assemblies according to the present
disclosure do not necessarily require a cooling system because of
their higher maximum operating temperature compared to conventional
windings based on polymer insulation. This opens up the option of
using alternative machine topologies (non-permanent magnet) such as
induction, switched reluctance, and synchronous electrical
machines. These have added advantages including: simpler operation,
no/reduced complexity converter and eliminated cooling system. This
results in less weight and a more power dense electrical
system.
Whilst the winding assembly 200 described with reference to FIGS. 2
to 4 is shown with one winding channel 204, the winding assembly
could be formed with multiple winding channels which are
direct-current (DC) electrically isolated from one another and are
therefore electrically separate windings of the electrical machine
in which the winding assembly is employed. In this manner, the 3D
printing process can be used to carefully control the geometry and
interplay of the different windings. For example, a bifilar winding
could be created from two separate channels inside the electrically
insulating body of the winding assembly. Whilst the electrically
insulating body provides DC electrical isolation between the two or
more windings it will still allow for inductive coupling between
windings.
An electric motor 103 comprising winding assemblies 200 of the type
described herein is particularly suitable for high speed, high
power output applications, for example in aerospace applications
where power to weight ratio is an important factor. Such an
electric motor 103 may therefore be suitable for use in electric
propulsion applications such as an electric propulsor 101 of the
type illustrated in FIG. 1. The propulsor 101 may further comprise
a gearbox 110 connected to receive an input from the electric motor
103 and to output drive to the fan 102 via shaft 104 so as to drive
the fan 102 at a lower rotational speed than the electric motor
103. The use of a gearbox 110 allows the electric motor to be
driven at higher speeds, thereby allowing the use of a smaller
motor for the same power output. Winding assemblies 200 according
to the present disclosure may also find application in other
machines having operating in a high temperature/voltage
environment, such as hybrid trains, electric turbocharging for
diesel engines and hybrid drives for yachts.
FIG. 6 is a flow chart corresponding to a method of manufacturing a
winding assembly for an electrical machine, the method
comprising:
S1: selecting a function defining the spatial separation between
adjacent turns of a winding path, the function dependent on one or
more parameters of the electrical machine and/or of the anticipated
operating environment of the electrical machine;
S2: forming, by three-dimensional, 3D, printing, an electrically
insulating body comprising a channel defining a winding path in
accordance with said function, the channel having an inlet and an
outlet;
S3: heating the electrically insulating body to a temperature above
the melting point of an electrically conducting material;
S4: flowing the electrically conducting material through the inlet
to the outlet to fill the channel; and
S5: cooling the electrically insulating body to solidify the
electrically conducting material within the channel, thereby
forming said winding assembly.
Step S2 may further comprise firing to densify the 3D printed
electrically insulating body, for example if the 3D printed body is
formed from a ceramic powder with a binder. As with conventional
ceramic processing, the binder may be removed by pyrolysis at
temperatures up to around 400 to 500 degrees Celsius, followed by
high temperature firing, typically at temperatures of over 1200
degrees Celsius, of the remaining ceramic material, the firing
temperature dependent on the type of ceramic material.
Whilst the winding assembly 200 described with reference to FIGS. 2
to 4 has a generally regular shape, the skilled person would
appreciate that the shape is not limited as such and instead it may
assume any shape as desired and which may be produced by a 3D
printing process.
Various examples have been described, each of which feature various
combinations of features. It will be appreciated by those skilled
in the art that, except where clearly mutually exclusive, any of
the features may be employed separately or in combination with any
other features and the invention extends to and includes all
combinations and sub-combinations of one or more features described
herein.
* * * * *